Our invention relates generally to apparatus for data transfer with record media such as, typically, flexible magnetic disks having a series of concentric data storage tracks on its surface. More specifically, our invention has to do with an electric control system for use in or with such magnetic disk apparatus, known also as a disk drive, for assuring the accurate writing on, and quick reading from, the disk medium. The invention may be considered an improvement of the disk drive control system suggested by Shoji et al. U.S. patent application Ser. No. 924,053 field Oct. 28, 1986.
In the flexible magnetic disk drive art in general, a stepper motor capable of rotation in short and essentially uniform angular movements is employed in combination with a motion translating mechanism such as a lead screw for transporting a transducer or transducers radially of the disk medium from track to track thereon. Stepped from one track to another, the transducer or transducers normally do not come to an immediate stop thereon but will oscillate or vibrate for some time before resting stably. We will refer to the time required for the travel of the transducer from one track to another as the "traveling time", and to the time during which the transducer oscillates or is otherwise unstable on the new track as the "settling time". The sum of the "traveling time" and the "settling time" is what we call "access time".
Should writing be commenced during the "settling time", that is, before the end of the "access time", then the written data might not subsequently be read correctly. The instruction manuals of some commercial disk drive models warn the user of this danger. However, this warning is to no effect in some instances.
Customarily, the disk drive is not self-contained; it is a slave unit under the control of a host system typically comprising a central processor unit and a disk drive controller. The host system may be conventionally programmed to commence writing immediately upon reception of the identification data on the magnetic disk from the disk drive. If the identification data is read and fed to the host system during the "access time", writing will start when the transducer is not yet stably positioned on the new track, resulting in the difficulties pointed out previously.
An attempted solution to this problem is found in the above cross-referenced Shoji et al. application Ser. No. 924,053. This prior application suggests the suppression of any identification data that may be read during the "settling time", as well as of the index pulses generated during the "access time". Accordingly, since the host system receives the identification data and index pulses only after the transducer has been stabilized on each new track, writing cannot possibly be started before the end of the "access time."
We have found the above solution unsatisfactory. Purely from the standpoint of accurate writing, the "settling time" and, therefore, the complete "access time" should be preset long enough to preclude the possibility of the incorrect reading of the identification data. The problem is that such long "access time" setting is an advantage from a viewpoint of accurate writing only and is a weakness from that of quick reading. This is because, according to the noted prior application, the read data output is suppressed during the "access time" not only in the write mode but also in the read mode. If the "access time" is determined long enough for the purpose of accurate writing, the possibility arises that data may be read correctly toward the end of each access time. The suppression of such possibly correctly read data during operation in the read mode runs counter to the objective of quick commencement of reading.